Composite containers that are used to contain gasses or liquids typically employ liners as a containment barrier and chemically-compatible surface material. These liners are either rigid, self-supporting shells or semi-rigid shells that may be pressure-stiffened. The rigid or rigidized liners are frequently used as a mandrel over which a reinforcing composite laminate is applied and cured to complete the container.
The liners in these applications serve a dual purpose by acting as rigid mandrel tooling for laminate application and as a containment barrier. Some of these liners may have sufficient structural strength to be classified as load-sharing (e.g., sharing the load with the laminate) while other liners are considered non-load-sharing. Load-sharing liners are often the most expensive component in the assembly and load-sharing liners typically represent a significant portion of the container's mass by having a greater thickness than would otherwise be required for non-load-sharing liners than are only utilized for barrier/compatibility purposes.
If, due to size or material properties, a liner cannot be readily rigidized or made to be self-supporting, a removable internal mandrel is used to support and maintain the shape of the liner during application of the structural laminate. Such mandrels can be costly, especially when needed for closed-end composite containers such as pressure vessels and tankage. An alternate approach for some large containers is to prefabricate the container's rigid laminate and secondarily apply a bond liner or surfacing material to the inner surface of the laminate. The liner in such an application is typically not continuous but is applied piecemeal, making integration labor intensive and subject to exposed bonded joints.
Another type of composite container developed primarily for cryogenic use is a linerless composite container. Linerless composite containers have been developed to avoid the mismatch between the coefficients of thermal expansion between a liner and reinforced laminate and the resultant thermally-induced stresses. These linerless composite containers rely on the laminate's matrix to provide a leak-free barrier. However, the resin systems tend to be brittle, particularly at low temperature where micro-cracking reduces the barrier integrity of the laminate's matrix.